Patent GB-1203821-A (GB)
Title: Systems for recording patterns on a record medium
IPC: H04N3/233
Filed: 1968-04-26
Abstract: 1,203,821. Cathode-ray tube displays. ALPHANUMERIC Inc. 26 April, 1968 [19 June, 1967], No. 19849/68. Heading H4T. In an arrangement for recording patterns, e.g. Alpha Numeric characters, on a moving record medium, the patterns, which are imaged on the record medium, being produced in the form of a line scanned rectangular raster on electromagnetic radiation source means, e.g. a cathode-ray display tube, with the line scans extending in the same direction as the motion of the record medium, " skew " of the patterns across the medium due to the motion of the latter is prevented by means which in response to the distance moved by the record medium, " offsets " the starting point of each line scan by a suitable amount. The invention is described in connection with a system in which Alpha Numeric characters, produced on the screen 20 (Fig. 1) of a cathode-ray tube CRT by ON-OFF control of the beam (Z axis) as it is swept vertically in a plurality of scans horizontally arrayed across a horizontal diameter region (" projection window ") 22, are imaged on to photographic film FLM which is moved by a speed controlled motor M in the same direction as the sweeps of the vertical scan. During each horizontal transverse of the vertical sweeps the movement of the film could cause a recorded line of characters such as line 24 to be " skewed " (i.e. to depart from the horizontal) and to prevent this the position, in the vertical direction, at which each scan commences is " offset " by an amount sufficient to compensate for such " skewing ".  The operation of the system is controlled by binary coded signals from a central Processor and Memory (CPM) which supplies signals controlling the vertical position of the " window " 22, Vertical Displacement Register (VDR), signals controlling the production of the vertical sweep, Vertical Sweep Gate Generator (VSG), signals controlling the required " offset ", Vertical Offset Counter (VOC), which also controls the speed and start-stop of the motor M via Film Motion control (FMC), together with signals controlling the horizontal deflection counter HDK and signals controlling the ONOFF condition of the beam Video Signal Generator, VG. In the operation of the system claimed counter VOC stores a count of pulses produced by a pulse generator PG controlled by movement of the film and representative of the distance through which the film has moved from a reference position (i.e. the start of a horizontal traverse) and supplies this count to the Vertical and Horizontal Deflection VHDS which converts it to an analogue signal and feeds it on line V to the vertical deflection yoke to " offset" the start of the vertical scanning sweeps by a corresponding distance. The general operation of the system having regard to this " offset " control feature is described. The Specification also describes a pin-cushion correction circuit included in the Vertical and Horizontal Deflection System VHDS. Referring to Fig. 5, the signals HDV, VDV and FPV (derived from counter HDK, register VDR and counter VOC, respectively. Fig. 1) are converted to analogue valves in respective converters 110, 118 and 124. The outputs of 118 and 124 are combined in amplifier 120 and fed to a scanning amplifier 130 (controlling the vertical deflection) and to an operation circuit 150 whilst the output of converter 110 is fed to amplifier 116 (controlling the horizontal deflection) and to an operation circuit 152. Assuming the deflection yokes and the tube screen to be linear, the pin-cushion distortion D is equal to AYX<SP>2</SP> and by generating an analogue voltage equivalent to this distortion and subtracting it from the vertical deflection signal, such distortion is corrected. Thus circuit 150 produces the function X<SP>2</SP> and circuit 152 (a linear amplifier) the function Y and these functions are then multiplied in circuit 158 which supplies a phase inverted output of the product to summing amplifier 130. This effects pin-cushion distortion correction as a function of the X and Y co-ordinates of the " base line ", i.e. the line from on which the vertical sweep deflection, which produce the character, commence and further correction is then required as a function of the length of the sweeps. This is effected by means of a peak detector 160 which produces a measure of the amplitude of the sweep signal from vertical sawtooth generator 132 and combines it in amplifier 164 with. vertical position signals (base line) from amplifier 120. The output of amplifier 164 is then fed to an operation circuit 168 together with the quantity X<SP>2</SP> from circuit 150 and the base line correction function 1/YX<SP>2</SP> from multiplier and inverter circuit 158. Circuit 168 then generates an analogue signal which is fed via line 136 to the sawtooth generator 132 to control the slope of the sawtooth wave the period of which is determined by the control pulses IHC from generator VSG (Fig. 1). Thus by controlling the slope of the sawtooth wave the length of the sweep is controlled as a function of the correction voltage from circuit 168. Details, in block diagram form, of the units FMC, PG and VSG of Fig. 1 are given with reference to Figs. 2, 3 and 4 respectively (not shown) and of the operation circuit 168 (Fig. 5) with reference to Figs. 6 and 7 (not shown). A circuit diagram of the sawtooth generator 132 (Fig. 5) is described with reference to Fig. 8  (not shown).